Seasonal and inter-annual variability of western subtropical mode water in the South Pacific Ocean
The seasonal and inter-annual variability of the western subtropical mode water (hereafter STMW) in the South Pacific Ocean was examined using the Bluelink ReANalysis 2.1 (BRAN2.1) in terms of heat budget. The analysis of heat content change suggested that the seasonal cycle of surface heat flux played a dominant role in the formation of the STMW in the South Pacific Ocean. However, the surface heat flux and the East Australian Current (EAC) heat transport tended to compensate one another during STMW production. Out of phase or different amplitude of the components led to warming or cooling of the mixed layer, and the heat transport by the EAC in the formation of the STMW cannot be ignored. The correlation between volume anomalies of the STMW and net surface heat flux was insignificant, indicating that the inter-annual variability of the STMW was equally influenced by surface thermal forcing and ocean dynamic processes, such as horizontal advection. This study revealed the important role played by the EAC in the inter-annual variability of the STMW, i.e., a weakened heat transport by the EAC led to an increased volume anomaly of the STMW in the South Pacific Ocean. The STMW production can be further enhanced by La Nina, which drives positive anomaly in sea surface salinity in the western South Pacific and creates a favourable preconditioning for surface cooling in austral winter.
KeywordsSubtropical mode water East Australian Current Bluelink reanalysis Seasonal variability Inter-annual variability Numerical modeling
The authors thank UNSW@ADFA RT scholarship program for funding this research. This work was also supported by the scientific research fund of the Second Institute of Oceanography, SOA (grant JT1007). The authors benefited from the comments of the three anonymous reviewers. The editorial assistance provided by Dr. Zuojun Yu is much appreciated. This is a publication of the Sino-Australian Research Centre for Coastal Management, paper number 18.
- Griffies SM, Harrison MJ, Pacanowski RC, Rosati A (2004) A technical guide to MOM4. NOAA/Geophysical Fluid Dynamics Laboratory, GFDL Ocean Group Technical Report No. 5: 371ppGoogle Scholar
- Levitus S (2001) World Ocean Database. vol. 13, U.S. Department of Commerce. National Oceanic and Atmospheric AdministrationGoogle Scholar
- Masuzawa J (1969) Subtropical mode water. Deep-Sea Res 16(5):463–468Google Scholar
- Schiller A, Smith N (2006) BLUELINK: Large-to-coastal-scale operational oceanography in the Southern Hemisphere, in Ocean Weather Forecasting: an integrated view of oceanography. Edited by Chassignet EP, Verron J, Springer International Press 427–439Google Scholar
- Talley LD (1999) Some aspect of ocean heat transport by the shallow, intermediate and deep overturning circulations. In: Mechanisms of global climate change and millennial time scales. P. Clark U, Webb RS, Keigwin LD (eds), Geophysical monograph series vol. 112 American Geophysical Union, Washington DC:1–22Google Scholar
- Tomczak M, Godfrey JS (1994) Regional oceanography: an introduction. Pergamon Press, Oxford, p 422Google Scholar
- Uppala SM, Kållberg PW, Simmons AJ, Andrae U, da Costa Bechtold V, Fiorino M, Gibson JK, Haseler J, Hernandez A, Kelly GA, Li X, Onogi K, Saarinen S, Sokka N, Allan RP, Andersson E, Arpe K, Balmaseda MA, Beljaars ACM, van de Berg L, Bidlot J, Bormann N, Caires S, Chevallier F, Dethof A, Dragosavac M, Fisher M, Fuentes M, Hagemann S, Hólm E, Hoskins BJ, Isaksen L, Janssen PAEM, Jenne R, McNally AP, Mahfouf JF, Morcrette JJ, Rayner NA, Saunders RW, Simon P, Sterl A, Trenberth KE, Untch A, Vasiljevic D, Viterbo P, Woollen J (2005) The ERA-40 re-analysis. Q J R Meteorol Soc 131(612):2961–3012CrossRefGoogle Scholar
- Warran BA (1972) Insensitivity of the mode water characteristics to meteorological fluctuations. Deep-Sea Res 19(1):1–19Google Scholar
- Worthington LV (1959) The 18 degree water in the Sargasso Sea. Deep-Sea Res 5(2–4):297–305Google Scholar